Microfeature workpieces having alloyed conductive structures, and associated methods

ABSTRACT

Microfeature workpieces having alloyed conductive structures, and associated methods are disclosed. A method in accordance with one embodiment includes applying a volume of material to a target location of a microfeature workpiece, with the volume of material including at least a first metallic constituent. The method can further include elevating a temperature of the volume of material while the volume of material is applied to the microfeature workpiece to alloy the first metallic constituent and a second metallic constituent so that the second metallic constituent is distributed generally throughout the volume of material. In further particular embodiments, the second metallic constituent can be drawn from an adjacent structure, for example, a bond pad or the wall of a via in which the volume of material is positioned.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 11/217,149filed Aug. 31, 2005, now U.S. Pat. No. 8,308,053, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention is directed generally toward microfeatureworkpieces having alloyed conductive structures, and associated methods,including associated methods of formation.

BACKGROUND

Microelectronic imagers are used in digital cameras, wireless deviceswith picture capabilities, and many other applications. Cell phones andPersonal Digital Assistants (PDAs), for example, are incorporatingmicroelectronic imagers for capturing and sending pictures. The growthrate of microelectronic imagers has been steadily increasing as theybecome smaller and produce better images with higher pixel counts.

Microelectronic imagers include image sensors that use Charged CoupledDevice (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS)systems, or other solid-state systems. CCD image sensors have beenwidely used in digital cameras and other applications. CMOS imagesensors are also quickly becoming very popular because they are expectedto have low production costs, high yields, and small sizes. CMOS imagesensors can provide these advantages because they are manufactured usingtechnology and equipment developed for fabricating semiconductordevices. CMOS image sensors, as well as CCD image sensors, areaccordingly “packaged” to protect their delicate components and toprovide external electrical contacts.

Many imaging devices include semiconductor dies having image sensorslocated on a front surface of the die to receive incoming radiation. Thedies also include bond pads for electrically coupling the sensors toother circuit elements. In order to prevent the bond pads frominterfering with the operation of the sensors, or limiting the sizeand/or location of the sensors, the bond pads are typically positionedon the opposite side of the die from the sensors (e.g., on the backsurface of the die). Through-wafer interconnects (TWIs) are used toconduct electrical signals from the sensors and associated internalcircuitry, through the die to the bond pads at the back surface. TheTWIs are typically formed by making a blind via in the die, filling thevia with solder, and then grinding the back surface of the die to exposethe blind end of the via, which is used to form the bond pad. A solderball can then be attached to the bond pad and can be reflowed to couplethe die to external devices.

One potential drawback associated with the foregoing approach is that,when the solder ball is later reflowed to electrically attach the die toexternal devices, the solder within the via may also tend to melt or atleast soften. During the ensuing attach process, the solder within thevia can be pulled at least partially out of the via, or can otherwiseundergo deformations and/or movement that can adversely affect theelectrical continuity of the TWI. In some instances, the electricalcontinuity of the TWI may be disrupted, causing the electricalconnection between the image sensor and the external devices to fail.Accordingly, there is a need for an improved arrangement for formingmicrofeature workpiece electrical connections, including connectionsbetween dies and external devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic, cross-sectional illustration of asubstrate prior to formation of a conductive structure in accordancewith an embodiment of the invention.

FIG. 1B is an enlarged view of a portion of the substrate shown in FIG.1A.

FIGS. 2A-2I illustrate a process for introducing a volume of material ina via and alloying the material in accordance with an embodiment of theinvention.

FIG. 3 is a phase diagram for a conductive material that includessilver, tin, and copper.

FIGS. 4A and 4B illustrate a process for completing an interconnectstructure shown in FIGS. 2A-2I.

FIG. 5 illustrates an imaging device that includes through-waferinterconnects configured in accordance with an embodiment of theinvention.

FIG. 6 illustrates a method for forming a through-wafer interconnect inaccordance with another embodiment of the invention.

FIGS. 7A and 7B illustrate a method for forming a conductive connectionat a bond pad in accordance with an embodiment of the invention.

FIGS. 8A and 8B illustrate a method for forming a conductive connectionat a bond pad in accordance with another embodiment of the invention.

DETAILED DESCRIPTION A. Overview/Summary

The following disclosure describes several embodiments of microfeatureworkpieces having alloyed conductive structures, and associated methodsfor forming such structures. One such method includes applying a volumeof material to a target location of a microfeature workpiece, with thevolume of material including at least a first metallic constituent. Themethod can further include elevating a temperature of the volume ofmaterial while the volume of material is applied to the microfeatureworkpiece to alloy the first metallic constituent and a second metallicconstituent so that the second metallic constituent is distributedgenerally throughout the volume of material.

In particular aspects of the invention, the target location can includea via extending through the microfeature workpiece. Applying a volume ofmaterial can include applying a volume of solder having a first metallicconstituent that includes an alloy of tin and silver. The secondmetallic constituent can include copper that is initially disposed as alayer on a wall of the via. The copper can alloy with the tin and silveras a result of elevating the temperature of the microfeature workpiece.The temperature can be elevated to be in the range of from about 240° C.to about 260° C. Alloying the first and second metallic constituents caninclude forming an alloy having a melting point that is higher than amelting point of the first metallic constituent alone. In still furtheraspects, the second metallic constituent can include gold. The methodcan further include dispersing silicon particulates in the volume ofmaterial (for example, while forming a via vent), and elevating atemperature of the volume of material can include alloying the siliconparticulates with the gold.

In yet further aspects, the target location can include a bond pad. Thevolume of material can alloy with a second metallic constituent that isreceived from the bond pad. Whether the target location includes a bondpad, via, or other structure, the second metallic constituent can belocated in the volume of material when the volume of material is appliedto the target location, and/or the second metallic constituent can belocated at the target location.

When the target location includes the second metallic constituent,alloying the first metallic constituent with at least a portion of thesecond metallic constituent can include alloying the first metallicconstituent with all of the second metallic constituent at the targetlocation. In other aspects, less than all of the second metallicconstituent at the target location can be alloyed with the firstmetallic constituent. In still further aspects, alloying the first andsecond metallic constituents can include alloying the first and secondmetallic constituents at a first rate, and the method can furthercomprise cooling the microfeature workpiece and continuing to alloy thefirst and second metallic constituents at a second rate less than thefirst rate.

A method for processing a microfeature workpiece in accordance with yetanother aspect of the invention includes applying a volume of materialbetween a first target location of a microfeature workpiece and a secondtarget location of a support member. The volume of material can includeat least a first metallic constituent. The method can further includeelevating a temperature of the volume of material while the volume ofmaterial is applied between the microfeature workpiece and the supportmember to alloy the first metallic constituent and a second metallicconstituent so that the second metallic constituent is distributedgenerally throughout the volume of material. The volume of material caninclude a volume of solder adjacent to a bond pad of the support member,with the bond pad including the second metallic constituent, andalloying the constituents can include alloying the first metallicconstituent with at least a portion of the second metallic constituentfrom the bond pad.

Further aspects of the invention are directed to microfeature systems. Amicrofeature system in accordance with one aspect includes amicrofeature workpiece having a surface with a first portion of ametallic constituent, wherein the metallic constituent is the second oftwo metallic constituents. The system can further include a volume ofmaterial positioned adjacent to the surface, the volume of materialincluding the first of the two metallic constituents, and furtherincluding a second portion of the second metallic constituentdistributed generally throughout the volume of material. The surfaceadjacent to which the volume of material is positioned can include thesurface of a bond pad or the surface of a via. In particular aspects,the volume of material can include solder, and the second metallicconstituent can include copper or gold.

A microfeature system in accordance with still another aspect of theinvention can include a microfeature workpiece having a conductivesurface, and a volume of material positioned adjacent to the conductivesurface. The volume of material can include first and second metallicconstituents, wherein the second metallic constituent includes at leastone percent copper by weight. In particular aspects, the volume ofmaterial can have a melting point of from about 240° C. to about 260°C., and the conductive surface can include a bond pad surface or a viasurface.

Specific details of several embodiments of the invention are describedbelow with reference to CMOS image sensors to provide a thoroughunderstanding of these embodiments, but other embodiments can use CCDimage sensors or other types of solid-state imaging devices. In stillfurther embodiments, aspects of the invention can be practiced inconnection with devices that do not include image sensors. As usedherein, the terms “microfeature workpiece” and “workpiece” refer tosubstrates on and/in which microfeature electronic devices (including,but not limited to, image sensors) are integrally formed. Typicalmicrofeature electronic devices include microfeature electronic circuitsor components, thin-film recording heads, data storage elements,microfluidic devices and other products. Micromachines andmicromechanical devices are included within this definition because theyare manufactured using much of the same technology that is used in thefabrication of integrated circuits. The substrates can besemi-conductive pieces (e.g., doped silicon wafers or gallium arsenidewafers), non-conductive pieces (e.g., various ceramic substrates) orconductive pieces. In some cases, the workpieces are generally round,and in other cases the workpieces can have other shapes, includingrectilinear shapes. Several embodiments of systems and methods forforming alloyed conductive structures in connection with microfeatureworkpiece fabrication are described below. A person skilled in therelevant art will understand, however, that the invention has additionalembodiments, and that the invention may be practiced without several ofthe details of the embodiments described below with reference to FIGS.1A-8B.

B. Methods for Forming Alloyed Conductive Structures

FIG. 1A is a side cross-sectional view of a portion of an imagerworkpiece 100 prior to the formation of conductive interconnectstructures in accordance with an embodiment of the invention. Theworkpiece 100 can include a substrate 101 with a plurality of imagingdies 120 formed in and/or on the substrate 101. The substrate 101 has afirst side or surface 102 and a second side or surface 103. Thesubstrate 101 can be a semiconductor wafer, with the imaging dies 120arranged in a die pattern on the wafer. Individual dies 120 can includeintegrated circuitry 121, a plurality of terminals or bond sites 122(e.g., bond pads) electrically coupled to the integrated circuitry 121with couplers 126, and an image sensor 112. The image sensors 112 can beCMOS image sensors or CCD image sensors for capturing pictures or otherimages in the visible spectrum. In other embodiments, the image sensors112 can detect radiation in other spectrums (e.g., IR or UV ranges). Thebond sites 122 shown in FIG. 1A are external features at the first side102 of the substrate 101. In other embodiments, however, the bond sites122 can be internal features that are embedded at an intermediate depthwithin the substrate 101. First and second dielectric layers 104 and 105can be located at the first side 102 to protect the underlying substrate101.

FIG. 1B is a side cross-sectional view of the area 1B shown in FIG. 1A.The second dielectric layer 105 has been patterned and etched to exposethe bond site 122. A mask 106 is applied over the second dielectriclayer 105 and patterned as shown in FIG. 1B. The mask 106 can be a layerof resist that is patterned according to the arrangement of bond sites122 on the substrate 101. Accordingly, the mask 106 can have an openingover each bond site 122.

Referring next to FIG. 2A, a via 130 has been formed in the workpiece100 so as to extend into the substrate 101 through the bond site 122 andthe first surface 102. The via 130 can be formed using any of a varietyof techniques, including etching or laser drilling. Further details ofmethods for forming the via 130 are disclosed in U.S. Patent ApplicationPublication No. 2006/0290001, which is incorporated herein by reference.A third dielectric layer 132 is deposited onto the workpiece 100 to linethe sidewalls 131 of the via 130 within the substrate 101. The thirddielectric layer 132 electrically insulates components in the substrate101 from an interconnect structure that is subsequently formed in thevia 130.

Referring to FIG. 2B, a suitable etching process (e.g., a spacer etch)is used to remove the third dielectric layer 132 from at least a portionof the bond site 122. Accordingly, this portion of the bond site 122 canbe exposed for electrical coupling to conductive structures in the via130.

As shown in FIG. 2C, a conductive barrier layer 133 is then depositedonto the workpiece 100 over the third dielectric layer 132 so as to bein electrical contact with the bond site 122. The barrier layer 133generally covers the second dielectric layer 105 and the bond site 122in addition to the third dielectric layer 132. In one embodiment, forexample, the barrier layer 133 is a layer of tantalum that is depositedonto the workpiece 100 using a physical vapor deposition (PVD) process.The thickness of the barrier layer 133 is about 150 Angstroms. In otherembodiments, the barrier layer 133 may be deposited onto the workpiece100 using other vapor deposition processes, such as chemical vapordeposition (CVD), and/or may have a different thickness. The compositionof the barrier layer 133 is not limited to tantalum, but rather may becomposed of tungsten or other suitable materials.

Referring next to FIG. 2D, a seed layer 134 is deposited onto thebarrier layer 133. The seed layer 134 can be deposited using vapordeposition techniques, such as PVD, CVD, atomic layer deposition, and/orplating. The seed layer 134 can be composed of copper or other suitablematerials. The thickness of the seed layer 134 may be about 2000Angstroms, but can be more or less depending upon the depth and aspectratio of the via 130. In several embodiments, the seed layer 134 may notuniformly cover the barrier layer 133 such that the seed layer 134 hasvoids 135 within the via 130. This can cause non-uniform electroplatingin the via 130 and across the workpiece 100. When the seed layer 134 isdeficient, it may be enhanced using a process that fills voids ornoncontinuous regions of the seed layer 134 to form a more uniform seedlayer. Referring to FIG. 2E, for example, voids 135 and/or noncontinuousregions of the seed layer 134 have been filled with additional material136, such as copper or another suitable material. One suitable seedlayer enhancement process is described in U.S. Pat. No. 6,197,181, whichis incorporated by reference.

Referring next to FIG. 2F, a resist layer 107 is deposited onto the seedlayer 134 and is patterned to have an opening 108 over the bond site 122and corresponding via 130. A first conductive layer 137 is thendeposited onto the exposed portions of the seed layer 134 in the via130. The first conductive layer 137 can include copper that is depositedonto the seed layer 134 in an electroless plating operation, or anelectroplating operation, or by another suitable method. In theillustrated embodiment, the thickness of the first conductive layer 137is about 1 micron. In other embodiments, the first conductive layer 137may include other suitable materials and/or have a different thickness.A second conductive layer 147 can then be deposited on the firstconductive layer 137. The second conductive layer 147 can include nickelor another adhesion barrier that prevents or restricts migration of thematerial (e.g., copper) in the first conductive layer 137.

A third conductive layer 148 can then be disposed on the secondconductive layer 147. The third conductive layer 148 can also includecopper. In particular embodiments, the third conductive layer 148 isconfigured so as to deliberately lose material during the formation ofan alloy in the via 130. Accordingly, the thickness of the thirdconductive layer 148 can be selected based on how much material from thethird conductive layer 148 is expected to be used up in the formation ofthe alloy. The second conductive layer 147 can act as a barrier toprevent a further loss of material from the first conductive layer 137.Alternatively, the second conductive layer 147 and the third conductivelayer 148 can be eliminated, and the first conductive layer 137 can bemade thick enough to withstand the loss of material during the alloyingprocess. Further details of an arrangement in which the second and thirdlayers are both present are described below with reference to FIGS. 2Hand 3. However, it will be understood that aspects of the invention mayalso be practiced with just the first conductive layer 137, provided itis thick enough. Further details of several embodiments for disposingthe conductive materials in the via 130 are disclosed in U.S. Pat. No.7,795,134, which is incorporated herein by reference.

Referring next to FIG. 2G, a vent hole 141 is formed in the substrate101 extending from the second side 103 of the substrate 101 to a bottomportion of the via 130. The vent hole 141 can be formed using a laserthat is aligned with the via 130 and/or the corresponding bond site 122using scanning/alignment systems known in the art. A suitable laser isthe Xise200, commercially available from Xsil Ltd. of Dublin, Ireland.After forming the vent hole 141, it is generally cleaned to removeablated byproducts (e.g., slag). For example, the vent hole 141 can becleaned using a suitable cleaning agent, such as 6% tetramethylammoniumhydroxide (TMAH): propylene glycol. In other embodiments, the vent hole141 may not be cleaned.

In several embodiments, a temporary protective filling or coating 139(shown in broken lines) can be deposited into the via 130 before formingthe vent hole 141. The protective filling 139 can be a photoresist, apolymer, water, a solidified liquid or gas, or another suitablematerial. The protective filling 139 protects the sidewalls of the via130 from slag produced during the laser drilling process. The slag cannegatively affect the wetting of a conductive fill material in the via130. The protective filling 139 can be removed after forming the venthole 141.

Referring next to FIG. 2H, a volume of material 140 (e.g., fillmaterial) is deposited into the via 130 to form an interconnectstructure 150. The interconnect structure 150 has a first end 142proximate to the bond site 122 and a second end 143 toward the bottom ofthe via 130. The material volume 140 can include a first metallicconstituent 144, shown schematically by open circles in FIG. 2H. Thefirst metallic constituent 144 can include a single metallic element, orin many cases, a mixture or alloy of multiple elements. For example, thefirst metallic constituent 144 can include a solder that in turnincludes one or more of tin, silver, copper, lead, gold and nickel. Insome embodiments, the entire material volume 140 can be comprised of thefirst metallic constituent 144 and in other embodiments, the materialvolume 140 can include substances in addition to the first metallicconstituent 144. The material volume 140 can be introduced into the via130 using plating processes (e.g., electroplating or electrolessplating), solder wave processes, screen printing processes, reflowprocesses, vapor deposition processes, or other suitable techniques.

Referring next to FIG. 2I, heat (indicated by arrows H) can be appliedto the material volume 140 to increase the temperature of the materialvolume 140 and, in at least some cases, melt or at least partiallyincrease the flowability of the material volume 140 and the firstmetallic constituent 144. The application of heat can also cause asecond metallic constituent 145 (shown schematically as speckles) toenter the material volume 140 from the third conductive layer 148. Forexample, when the third conductive layer 148 includes copper, at least aportion of the copper can enter the material volume 140. Moreover, thesecond metallic constituent 145 can dissolve into, alloy with, and/orotherwise chemically bond with the first metallic constituent 144. Thealloyed first metallic constituent 144 is shown schematically by solidcircles in FIG. 2I. In so doing, the second metallic constituent 145 canbecome generally distributed throughout the material volume 140. As usedherein, the term “generally distributed” refers to a distribution thatextends beyond just the interface between the material volume 140 andthe third conductive layer 148. The term “generally distributed”includes, but is not limited to, a uniform distribution.

The amount of the second metallic constituent 145 that alloys with thefirst metallic constituent 144 can be controlled by several factors,including the temperature to which the material volume 140 and the thirdconductive layer 148 are elevated, and the amount of the second metallicconstituent 145 available from the third conductive layer 148. Theeffects of these characteristics can be illustrated with an appropriatephase diagram. FIG. 3 is a phase diagram illustrating properties of asilver/tin/copper alloy. The vertical axis identifies the masspercentage of silver in the alloy, the horizontal axis identifies themass percentage of copper in the alloy, and lines of constant meltingpoint temperature are identified by the corresponding temperaturevalues. Accordingly, FIG. 3 illustrates aspects of an alloying processthat is carried out when the first metallic constituent 144 includes analloy of tin and silver, and the second metallic constituent 145includes copper.

Referring now to FIGS. 2I and 3 together, elevating a temperature of theworkpiece 100 to about 240° C. will result in an alloy having about 1.2%copper. If the original material volume 140 includes less than 1.2%copper, then additional copper may be withdrawn from the thirdconductive layer 148. After cooling the microfeature workpiece 100, thesubsequent melting point for the material volume 140 will be at least240° C. In fact, in at least some embodiments, additional alloying maycontinue at lower temperatures (including room temperature), assuming anadditional amount of the second metallic constituent 145 is availablefrom the third conductive layer 148. Additional alloying may also occurduring subsequent processes for which the temperature of themicrofeature workpiece 100 is elevated.

In another example, the temperature of the microfeature workpiece 100can be elevated to about 260° C. At this temperature, the resultingalloy in the material volume 140 can include about 1.6% copper. Thesubsequent melting point for the material volume 140 will be at least260° C., which as described above, can increase over time due tocontinued alloying. In at least one embodiment, the alloy of the firstand second metallic constituents 144, 145 can include at least 1% copperby weight. In other embodiments, the amount of the second constituent145 can differ depending, for example, on the chemical makeup of boththe first and second metallic constituents 144, 145.

Another method for controlling the amount of the second metallicconstituent 145 that alloys with the first metallic constituent 144 isto control the thickness of the third conductive layer 148. For example,if the third conductive layer 148 includes copper, but includes onlyenough copper to provide an alloy that is about 1.2% copper, then,assuming the temperature of the workpiece 100 is elevated to at least240° C., the amount of copper alloying with the first metallicconstituent 144 will be limited to about 1.2%, even if subsequent lowtemperature or high temperature alloying is conducted. In other words,the entire volume of the third conductive layer 148 will enter into thematerial volume 140 to form an alloy. Conversely, if the thirdconductive layer 148 includes more of the second metallic constituent145 than can alloy with the first metallic constituent 144 at a giventemperature, then the amount of the second metallic constituent 145alloying with the first metallic constituent 144 may be limited by thetemperature at which the process is conducted. In this case, a firstportion of the second metallic constituent 145 will migrate to thematerial volume 140, and a second portion will remain in the conductivelayer 137.

The end result of an alloying process in accordance with several of theforegoing embodiments is that the melting point of the material volume140 and/or the temperature at which the flowability of the materialvolume 140 increases, will be elevated. Accordingly, the material volume140 will be less likely to melt or otherwise flow during subsequentprocesses that include heating the microfeature workpiece 100. Asdescribed further below, such processes can include attaching solderballs to the interconnect structure 150, and/or reflowing the solderballs to provide electrical connections to external devices.

FIGS. 4A and 4B illustrate further manufacturing processes conducted tocomplete the formation of the microfeature workpiece 100. Referringfirst to FIG. 4A, the resist layer 107 shown in FIG. 2I can be removedfrom the substrate 101, and a suitable etching process can be used toremove the remaining portions of the seed layer 134 and the barrierlayer 133 on the first side 102 of the substrate 101. The first side 102of the substrate 101 can be planarized using a grinding, chemicalmechanical planarization (CMP), and/or other suitable process. The via130 can initially be a blind via that can be made to extend entirelythrough the substrate 101 by a back grinding process, as described infurther detail below with reference to FIG. 4B.

FIG. 4B illustrates the substrate 101 after material has been removedfrom the second surface 103 to expose the second end 143 of theinterconnect structure 150. Accordingly, the second end 143 of theinterconnect structure 150 can form a second bond site 146 to which asolder ball or other conductive coupler 111 can be attached for couplingthe workpiece 100 to external devices. The solder ball 111 can have alower melting point than that of the alloyed material volume 140.Accordingly, when the temperature of both the material volume 140 andthe solder ball 111 are elevated to attach the solder ball 111, thematerial volume 140 will be less likely to melt, flow or otherwisebecome displaced from the via 130.

FIG. 5 is a partially schematic illustration of a finished imagingdevice 510 configured in accordance with an embodiment of the invention.The imaging device 510 can include a die 520 having an integratedcircuit 521 coupled to an image sensor 512, which can in turn include anarray of pixels 570 arranged in a focal plane. A color filter array(CFA) 513 is positioned over the pixels 570 of the sensor 512. The CFA513 has individual filters or filter elements 571 configured to allowthe wavelengths of light corresponding to selected colors (e.g., red,green, or blue) to pass to each pixel 570 of the image sensor 512. Inthe illustrated embodiment, for example, the CFA 513 is based on the RGBcolor model, and includes red filters, green filters, and blue filtersarranged in a desired pattern over the corresponding pixels 570. The CFA513 can further include a residual blue section 572 that extendsoutwardly from a perimeter portion of the image sensor 512. The residualblue section 572 helps prevent back reflection from the variouscomponents within the die 510.

The imaging device 510 can further include a plurality of microlenses514 arranged in a microlens array 515 over the CFA 513. The microlenses514 are used to focus light onto the initial charge accumulation regionsof the image sensor pixels 513. Standoffs 573 are positioned adjacent tothe microlens array 515 to support a transmissive element 516. Thetransmissive element 516 (which can include glass) is positioned toprotect the microlens array 515 and other features of the die 520 fromcontamination. Lens standoffs 574 can be mounted to the transmissiveelement 516 to support a device lens 517. The device lens 517 ispositioned a selected distance away from the microlens array 515 tofocus light onto the microlens array 515 and ultimately onto the imagesensor 512.

As is also shown in FIG. 5, the imaging device 510 can be attached to anexternal device 560, for example, a support member 561 (e.g., a printedcircuitboard) having support member bond pads 562. The imaging device510 can be attached to the support member 561 by (a) screen printing orotherwise applying a solder brick 563 (e.g., a combination of solder andflux) to the bond pads 562, (b) contacting the solder balls 511 with thesolder bricks 563, and (c) applying heat so as to reflow or otherwisesoften the solder balls 511 and the solder bricks 563. As describedabove with reference to FIG. 4B, the solder balls 511 can have a meltingpoint that is lower than the melting point of the alloyed materialvolume 140. Accordingly, the material volume 140 can be less likely toflow during the attachment process and, as a result, the material volume140 can be less likely to be pulled from the via in which it is placed.In a further aspect of this embodiment, material in the solder balls 511(e.g., a first metallic constituent 144 such as tin/silver) can alloywith a second metallic constituent 145 (e.g., copper) present in thematerial volume 140. Accordingly, the melting point of the solder ball511 can be raised during this process, making the solder ball 511 lesslikely to reflow or otherwise become displaced during subsequent hightemperature processes.

In still a further aspect of an embodiment shown in FIG. 5, the solderbricks 563 can undergo a similar alloying process. For example, thesolder bricks 563 can include a first metallic constituent 144 (e.g., atin/silver alloy) that further alloys with a second metallic element 145(e.g., copper) from the support member bond pads 562. As a result, thesolder bricks 563 will also be less likely to become displaced duringsubsequent high temperature processes. Such subsequent processes caninclude attaching the support member 561 to other external devices.

One feature of at least some embodiments of the workpieces andassociated formation techniques described above is that they can includeelevating the melting point of the material volume 140 in the via 130 byalloying the first and second metallic constituents 144, 145. As wasalso described above, an advantage of the arrangement is that thematerial volume 140 will be less likely to become displaced (as a resultof softening or melting) during subsequent high temperature processes.Accordingly, the reliability of the microfeature workpiece in which thematerial volume 140 is disposed can be increased.

Another feature of at least some embodiments of the workpieces andassociated formation techniques described above is that they can includepositioning a copper layer (e.g., the third conductive layer 148) indirect contact with a solder volume (e.g., the material volume 140).This is in direct contrast to at least some existing TWI structures, inwhich a nickel layer is positioned adjacent to the fill material in thevia. Unlike existing TWI structures, in at least one aspect of thepresent invention, copper migration may be facilitated so as to producethe desired alloy in the via.

In one aspect of an embodiment described above with reference to FIG.2G, a protective filling 139 was positioned in the via 130 to protectthe interior of the via from debris that might be deposited in the via130 as a result of forming the vent hole 141. In an embodiment shown inFIG. 6, the protective filling 139 was not used, or did not completelyprevent particulates 638 from being directed into the via 130. Theparticulates 638 can include particulates of the substrate 101, forexample, silicon particulates. In a particular aspect of the embodimentshown in FIG. 6, the workpiece 100 can include a conductive layer 637that includes a second metallic constituent 645 selected to alloy withthe particulates 638. For example, in one aspect of this embodiment, theconductive layer 637 can include gold, which, at elevated temperatures,can alloy with the silicon particulates 638. The gold can also alloywith the first metallic constituent 144 located in the material volume140. An advantage of this arrangement is that it can reduce or eliminatethe potential negative impact of the particulates 638 in the via 130. Inanother aspect of this embodiment, the conductive layer 637 is thickenough to undergo the alloying process without exposing the underlyingseed layer 134. Accordingly, the substrate need not include the nickellayer described above with reference to FIG. 2H.

One aspect of several of the embodiments described above is that thematerial volume 140 was disposed adjacent to the walls of a via 130prior to being alloyed with the second metallic constituent 145. Inother embodiments, the material volume can be located adjacent to otherstructures of the microfeature workpiece. For example, the materialvolume can include the solder balls 511 and/or the solder bricks 563,either or both of which may undergo an alloying process, as describedabove with reference to FIG. 5. In still further embodiments, thealloying process can be used in other contexts. For example, referringnow to FIG. 7A, a microfeature workpiece 700 can include a substratematerial 701 in which a conductive line 718 and a corresponding via 730have been formed to electrically connect to a bond pad 719 located at abond site 722. The bond pad 719 can include a second metallicconstituent 745, and a material volume 740 (e.g., a solder ball 711) caninclude a first metallic constituent 744. The bond pad 719 can initiallyhave a thickness T1.

Referring next to FIG. 7B, heat H can be applied to the microfeatureworkpiece 700, in some cases causing the material volume 740 to melt orat least soften. As described above, the heat can also cause the secondmetallic constituent 745 to dissolve from the bond pad 719 into thematerial volume 740 and alloy with the first metallic constituent 744.The results of the foregoing operation can include a reduction in thethickness of the bond pad 719 from the initial thickness T1 (FIG. 7A) toa reduced thickness T2.

FIG. 8A illustrates the microfeature workpiece 700 having a bond pad 819and a material volume 840 configured in accordance with anotherembodiment of the invention. In one aspect of this embodiment, thematerial volume 840 can include both the first metallic constituent 744and the second metallic constituent 745. The bond pad 819 can include nosecond metallic constituent 745 (as shown in FIG. 8A), or it canoptionally include an additional amount of the second metallicconstituent 745 (as was generally shown in FIG. 7A). When heat isapplied to the microfeature workpiece 700 (as shown in FIG. 8B), thefirst metallic constituent 744 can alloy with the second metallicconstituent 745. If the bond pad 819 does not include the secondmetallic constituent 745, or if the amount of the second metallicconstituent 745 in the material volume 840 is at or above a saturationlevel, then the thickness of the bond pad 819 is not expected to changeas a result of the heating process. Otherwise, the thickness of the bondpad 819 can reduce in a manner generally similar to that described abovewith reference to FIG. 7B.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from theinvention. For example, the material volume can be applied to sites ofthe workpiece other than an interconnect structure or a bond pad. Thefirst and second metallic constituent can include elements and/or alloysother than those specifically identified above. In particularembodiments, the second metallic constituent can include multipleelements (e.g., copper and gold). In other embodiments, the conductivelayers in the via can include successively sputtered layers of chrome,chrome/copper and then copper. Aspects of the invention described in thecontext of particular embodiments may be combined or eliminated in otherembodiments. For example, a material volume that includes both the firstand second metallic constituents, described in the context of FIGS. 8Aand 8B, can be applied equally to the material volume described withreference to FIG. 2G. Further, while advantages associated with certainembodiments of the invention have been described in the context of thoseembodiments, other embodiments may also exhibit such advantages, and notall embodiments need necessarily exhibit such advantages to fall withinthe scope of the invention. Accordingly, the invention is not limitedexcept as by the appended claims.

We claim:
 1. A microfeature system, comprising: a microfeature workpiecehaving a surface; a via extending from the surface into the microfeatureworkpiece; a first conductive material lining the via; a secondconductive material on the first conductive material, wherein the secondconductive material is positioned to restrict migration of the firstconductive material through the second conductive material; a thirdconductive material on the second conductive material, the thirdconductive material having a first portion of a metallic constituent,the metallic constituent being the second of two metallic constituents;and a volume of material positioned at least partially in the via, thevolume of material including the first of the two metallic constituents,the volume of material further including a second portion of the secondmetallic constituent distributed generally throughout the volume ofmaterial.
 2. The system of claim 1 wherein the surface includes asurface of a bond pad.
 3. The system of claim 1 wherein the volume ofmaterial includes a volume of solder.
 4. The system of claim 1 whereinthe second metallic constituent includes copper.
 5. The system of claim1 wherein the second metallic constituent includes gold.
 6. The systemof claim 1 wherein the first metallic constituent includes at least oneof tin and silver.
 7. The system of claim 1 wherein the surface is aconductive surface and wherein the microfeature workpiece includes afirst major surface and a second major surface facing opposite from thefirst major surface, and wherein the conductive surface includes asurface of the via extending through the microfeature workpiece from thefirst major surface to the second major surface, and wherein the volumeof material includes a volume of solder positioned in the via.
 8. Thesystem of claim 1 wherein the first metallic constituent includes solderand wherein the second metallic constituent includes copper, furtherwherein the copper at the surface of the microfeature workpiece is indirect contact with the solder.
 9. The system of claim 1 wherein thevolume of material has a melting point of from about 240° C. to about260° C.
 10. A microfeature system, comprising: a microfeature workpiecehaving a conductive surface; a via extending from the surface into themicrofeature workpiece; a first conductive material lining the via; asecond conductive material on the first conductive material, wherein thesecond conductive material is positioned to restrict migration of thefirst conductive material through the second conductive material; athird conductive material on the second conductive material, the thirdconductive material having a first portion of a metallic constituent,the metallic constituent being the second of two metallic constituents;and a volume of material positioned adjacent to the conductive surface,the volume of material including first and second metallic constituents,wherein the second metallic constituent includes at least 1% copper byweight.
 11. The system of claim 10 wherein the conductive surfaceincludes a surface of a bond pad.
 12. The system of claim 10 wherein thevolume of material has a melting point of from about 240° C. to about260° C.
 13. The system of claim 10 wherein the first metallicconstituent includes solder.
 14. The system of claim 10 wherein thefirst metallic constituent includes solder, and wherein the solderincludes silver and tin.
 15. The system of claim 10 wherein the surfaceis a conductive surface and wherein the microfeature workpiece includesa first major surface and a second major surface facing opposite fromthe first major surface, and wherein the conductive surface includes asurface of the via extending through the microfeature workpiece from thefirst major surface to the second major surface, and wherein the volumeof material includes a volume of solder positioned in the via.
 16. Amicrofeature system, comprising: a microfeature workpiece having asurface; a via extending from the surface into the microfeatureworkpiece; a first conductive material lining the via; a secondconductive material on the first conductive material, wherein the secondconductive material is positioned to restrict migration of the firstconductive material through the second conductive material; a thirdconductive material on the second conductive material, the thirdconductive material having a first portion of a metallic constituent,the metallic constituent being the second of two metallic constituents;and a volume of material positioned at least partially in the via, thevolume of material including the first of the two metallic constituents,the volume of material further including a second portion of the secondmetallic constituent distributed generally throughout the volume ofmaterial, wherein the first metallic constituent is different than thesecond metallic constituent.